A conventional harrow implement includes a tool bar extending perpendicular to the implement's operating travel direction and a plurality of harrow sections extending rearward from the tool bar and movably mounted to the tool bar such that the harrow sections can move up and down so the harrow tines thereof can bear against the ground. The tool bar typically has a center section and right and left wing sections which can be folded, typically rearward, to a transport position.
A typical harrow section comprises rearward extending frame arms, and a plurality of support bars attached to the frame arms. The support bars are oriented perpendicular to the frame arms and perpendicular to the operating travel direction, and are equally spaced along the frame arms. Flexing harrow tines are attached to each support bar, and the support bars are rotatable with respect to the frame arms to adjust the tine angle of the harrow tines with respect to the ground.
The pitch angle of the frame arms is typically adjustable as well by raising or lowering either the front or rear of the frame arms to have the front harrow tines bear down against the ground to a greater or lesser extent compared to the rear harrow tines.
The harrow sections are also pushed downward toward the ground with a bias system that transfers weight from the tool bar to the harrow sections. The bias system is typically a spring arrangement, that can be adjusted to vary the bias force.
Provision is also made to move the harrow sections to a raised transport position extending upright from the tool bar which allows the wing sections of the tool bar to fold to a rearward trailing transport position.
U.S. Pat. No. 5,492,182 to Delaurier discloses a harrow implement where the bias force is provided by a spring attached to the tool bar which exerts an upward force on the harrow frame forward of a pivot axis about which the harrow frame is attached to the tool bar such that the harrow frame is pushed downward.
U.S. Pat. No. 6,164,386 to Delaurier discloses a harrow implement where the bias force is provided by a spring attached to the tool bar which exerts a direct downward force on the harrow frame rearward of the pivot axis about which the harrow frame is attached to the tool bar such that the harrow frame is pushed downward.
In the Delaurier disclosures the harrow frames are pivotally attached to the tool bar about a single pivot axis so that as the harrow frame pivots up and down the pitch angle varies as the rear end thereof, farther from the pivot axis moves up and down to a greater degree than the front end there which is near the pivot axis. In contrast in the harrow implement disclosed in U.S. Pat. No. 8,657,026 to Friesen, which discloses a tine angle adjustment system using hydraulic cylinders, the harrow frames are pivotally attached to the tool bar by a parallel link assembly such that the pitch angle remains constant as the harrow frames pivot up and down.
U.S. Pat. No. 5,622,229 to Degelman discloses a harrow implement with spring straps extending rearward of the tool bar. The harrow frames can be attached directly to the spring straps to allow the harrow frames to move up and down and also provide the desired downward bias force on the harrow sections. In another embodiment the harrow frame is pivotally attached to the tool bar and the spring straps provide the desired downward bias force.